Method of preparing a coated abrasive article that incorporates an energy cured make coat

ABSTRACT

A coated abrasive article comprises a backing, a first binder on the backing, and a plurality of abrasive particles in the first binder. The first binder is a hot melt pressure sensitive adhesive that is energy cured to provide a crosslinked coating. The invention also relates to a method of producing such articles.

This is a division of application Ser. No. 08/047,861 filed Apr. 15,1993, now U.S. Pat. No. 5,436,063.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to coated abrasive articles and, moreparticularly, to such articles which incorporate an energy cured hotmelt make coat.

2. Description of the Related Art

Coated abrasive articles generally comprise a backing layer to which amultiplicity of abrasive particles are bonded. In one form, the abrasiveparticles are bonded to the backing by a first binder, commonly referredto as a make coat. A second binder, commonly called a size coat, is thenapplied over the make coat and the abrasive particles to reinforce theparticles. In a second form, the abrasive particles are dispersed in abinder to provide an abrasive composite and the composite is bonded tothe backing by the binder.

Porous cloth, fabric and textile materials are frequently used asbackings for coated abrasive articles. The make coat is typicallyapplied to the backing as a low viscosity material. In this condition,the make coat can migrate into the backing and accumulate in theinterstices formed by the intersecting warp and fill fibers of theporous backing. This can result in the backing becoming stiff, hard andbrittle with a consequent loss of its natural pliability. However,flexible, pliable, coated abrasive articles are desired. As a result, ithas become conventional to employ a presize or saturant coat to seal theporous backing even though this added processing step increases the costand complexity of manufacturing.

U.S. Pat. No. 4,163,647 "Method for Producing Coated Abrasive," issuedAug. 7, 1979 to H. J. Swiatek proposes coating a cloth backing materialon its front side with a liquid thermosetting resin in such a mannerthat the resin does not permeate the interstices of the cloth. Suggestedliquid thermosetting resins include heat hardenablephenol-formaldehydes.

U.S. Pat. No. 4,751,138 "Coated Abrasive Having Radiation CurableBinder," issued Jun. 14, 1988 to M. L. Tumey et al. discloses aradiation curable epoxy-based make coat. Reportedly, the radiationcurable composition can be used to treat the backing material; forexample, by saturating it or providing a front coat therefor.

U.S. Pat. No. 4,927,431 "Binder for Coated Abrasives," issued May 22,1990 to S. J Buchanan et al. discloses an abrasive product whichutilizes a binder formed from a blend of a radiation curable monomer anda thermally curable resinous material. The binder bonds abrasive grainsto a major surface of a backing sheet and can also function as a backingtreatment for the coated abrasive article.

U.S. Pat. No. 4,240,807 "Substrate Having a Thermoplastic Binder Coatingfor Use in Fabricating Abrasive Sheets and Abrasive Sheets ManufacturedTherewith," issued Dec. 23, 1980 to F. J. Kronzer discloses a flexiblebacking material which has a heat activated binder on one surfacethereof. The binder is reportedly a nontacky solid at ambienttemperatures, but when heated is converted to a viscous fluid thatpermits abrasive grains deposited thereon to sink into the coating to adepth which provides a firm bond therewith. When the heat is removed,the coating reverts to its solid nontacky state.

However, there remains considerable need for a make coat which can bereadily applied to a porous cloth, fabric or textile backing without theneed for a separate presize or saturant coat to seal the backing.

SUMMARY OF THE INVENTION

In general, this invention relates to a coated abrasive article thatcomprises a backing, a first binder or make coat on the backing, and aplurality of abrasive particles in the first binder. Many of the coatedabrasive articles further include a second binder, such as a glue or acured resinous adhesive, over the first binder and the abrasiveparticles, as well as a third binder over the second binder.

The first binder is a hot melt pressure sensitive adhesive that has beenenergy cured to provide a crosslinked coating. Because the first binderis a hot melt composition it is particularly useful with porous cloth,textile or fabric backings. The first binder does not penetrate theinterstices of the porous backing, thereby preserving the naturalflexibility and pliability of the backing.

In a broad aspect of the invention, the first binder comprises anepoxy-containing material, a polyester component, and an effectiveamount of an initiator for energy curing the binder. More particularly,the first binder comprises from about 2 to 95 parts of theepoxy-containing material and, correspondingly, from about 98 to 5 partsof the polyester component, as well as the initiator. An optionalhydroxyl-containing material having a hydroxyl functionality greaterthan 1 may also be included.

Preferably, the polyester component has a Brookfield viscosity whichexceeds 10,000 milliPascals at 121° C. with a number average molecularweight of about 7500 to 200,000, more preferably from about 10,000 to50,000, and most preferably from about 15,000 to 30,000. The polyestercomponent may be the reaction product of a dicarboxylic acid selectedfrom the group consisting of saturated aliphatic dicarboxylic acidscontaining from 4 to 12 carbon atoms (and diester derivatives thereof)and aromatic dicarboxylic acids containing from 8 to 15 carbon atoms(and diester derivatives thereof) and (b) a diol having 2 to 12 carbonatoms.

The optional hydroxyl-containing material more preferably has a hydroxylfunctionality of at least 2 and even more preferably a hydroxylfunctionality of about 3. Particularly preferred materials arepolyoxyalkylene polyols such as polyoxyethylene glycols andpolyoxypropylene glycols having a number average equivalent weight ofabout 31 to 2250, and polyoxyethylene triols and polyoxypropylene triolshaving a number average equivalent weight of about 80 to 350.Polyoxyalkylene polyols are especially preferred when the initiator isan aromatic sulfonium complex salt or an aromatic iodonium complex salt.Also useful is cyclohexane dimethanol, especially if the initiator is ametallocene salt. The hydroxyl-containing material is useful inenhancing the flexibility of the first binder and can sufficientlyretard the curing reaction after the first binder has been exposed toenergy so as to permit abrasive particles to be adhered thereto.

In more preferred first binders, the epoxy-containing material comprisesfrom 2 to 80 parts thereof and the polyester component comprises,correspondingly, from 98 to 20 parts thereof. Even more preferred arefirst binders comprising from 2 to 60 parts of the epoxy-containingmaterial and, correspondingly, from 98 to 40 parts of the polyestercomponent.

The invention also relates to a method of providing such coated abrasivearticles. The energy curable, hot melt pressure sensitive first binderis applied (preferably by coating) to the backing and is exposed toenergy (preferably actinic radiation). A plurality of abrasive particlesis deposited in the first binder either before after it is exposed toenergy. The binder is then permitted to cure to a crosslinked coating.The pressure sensitive properties of the first binder (before it finallycures) permits the abrasive particles to adhere thereto. The firstbinder can be thermally postcured.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood with reference to thefollowing drawings in which similar reference numerals designate like oranalogous components throughout and in which:

FIG. 1 is a perspective view of a coated abrasive article according tothe invention; and

FIG. 2 is a sectional view of a coated abrasive article according to theinvention and taken along lines 2--2 of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings, FIGS. 1 and 2 illustrate a coated abrasivearticle 10 according to the invention comprising a backing 12 and anabrasive layer 14 bonded thereto.

Backing 12 may be comprised of cloth, vulcanized fiber, paper, nonwovenmaterials, polymeric films, and laminated multilayer combinationsthereof. Cloth backings may be woven or stitch bonded and may includefibers or yarns of cotton, polyester, rayon, silk, nylon or blendsthereof. Nonwoven backings may comprise cellulosic fibers, syntheticfibers or blends thereof. As explained below, porous cloth, fabric ortextile backings are especially advantageously employed in the coatedabrasive articles of the invention.

Abrasive layer 14 comprises a multiplicity of abrasive particles 16which are bonded to a major surface of backing 12 by a first binder ormake coat 18. A second binder or size coat 20 is applied over theabrasive particles and the make coat to reinforce the particles. Theabrasive particles typically have a size of about 0.1 to 1500 microns(μm), more preferably from about 1 to 1300 μm. Preferably the abrasiveparticles have a MOH hardness of at least about 8, more preferablygreater than 9. Examples of useful abrasive particles includealuminum-oxide based materials (e.g., aluminum oxide, ceramic aluminumoxide (which may include one or more metal oxide modifiers), and heattreated aluminum oxide), silicon carbide, confused alumina-zirconia,diamond, ceria, cubic boron nitride, garnet and blends thereof. Abrasiveparticles also include abrasive agglomerates such as disclosed in U.S.Pat. No. 4,652,275 and U.S. Pat. No. 4,799,939, which patents are herebyincorporated by reference.

First binders useful in the coated abrasive articles of the inventioncomprise a hot melt pressure sensitive adhesive composition that curesupon exposure to energy to provide a covalently crosslinked, thermosetmake coat. Because the make coat can be applied as a hot meltcomposition, it does not readily penetrate the backing so as tocompromise the backing's inherent pliability and flexibility.Consequently, the make coats disclosed herein are particularlyadvantageous when employed in conjunction with porous cloth, fabric ortextile backings.

By "porous" is meant a backing not having an abrasive layer, a makecoat, an adhesive layer, a sealant, a saturant coat, a presize coat, abacksize coat, etc. thereon and which demonstrates a Gurley porosity ofless than 50 seconds when measured according to Federal Test Method Std.No. 191, Method 5452 (published Dec. 31, 1968) (as referred to in theWellington Sears Handbook of Industrial Textiles by E. R. Kaswell, 1963edition, page 575) using a Gurley Permeometer (available from TeledyneGurley, Inc., Troy, N.Y.). Cloth backings of presently known coatedabrasive articles conventionally require special treatments such as asaturant coat, a presize coat, a backsize coat or a subsize coat toprotect the cloth fibers and to seal the backing. Coated abrasivearticles according to the invention, however, require no such treatment,yet remain durable and flexible. While the coated abrasive articles ofthe invention do not require these treatments, they may be provided, ifdesired. The hot melt make coats of the invention can provide suchtreatments.

The pressure sensitive adhesive qualities of the hot melt make coatenable the abrasive particles to adhere to the make coat until the sizecoat is applied thereover. The crosslinked, thermoset make coat istough, yet flexible, and aggressively adheres to the backing.

As used herein, a "hot melt" composition refers to a composition that isa solid at room temperature (about 20° to 22° C.) but which, uponheating, melts to a viscous liquid that can be readily applied to acoated abrasive article backing. Desirably, the hot melt make coats ofthe invention can be formulated as solvent free systems (i.e., they haveless than 1% solvent in the solid state). As used herein, a "pressuresensitive adhesive" refers to a hot melt composition that, at the timeabrasive particles are applied thereto, displays pressure sensitiveproperties. Pressure sensitive properties means that in response to theapplication of at least light pressure, the composition is tackyimmediately after application to a backing and while still warm and, insome cases, even after it has cooled to room temperature.

The hot melt make coats useful in the invention comprise and, morepreferably, consist essentially of, an epoxy-containing material thatcontributes to the toughness and durability of the make coat, apolyester component that allows for the make coat to display pressuresensitive properties, and an initiator that permits the composition tocure upon exposure to energy. Optionally, though quite desirably, thehot melt make coats of the invention may also include ahydroxyl-containing material to retard the rate of curing and/or impartflexibility to the make coats.

Epoxy-containing materials useful in the make coats of the invention areany organic compounds having at least one oxirane ring ##STR1##polymerizable by a ring opening reaction. Such materials, broadly calledepoxides, include both monomeric and polymeric epoxides and can bealiphatic, cycloaliphatic, or aromatic. They can be liquid or solid orblends thereof, blends being useful in providing tacky adhesive films.These materials generally have, on the average, at least two epoxygroups per molecule (preferably more than two epoxy groups permolecule). The polymeric epoxides include linear polymers havingterminal epoxy groups (e.g., a diglycidyl ether of a polyoxyalkyleneglycol), polymers having skeletal oxirane units (e.g., polybutadienepolyepoxide), and polymers having pendent epoxy groups (e.g., a glycidylmethacrylate polymer or copolymer). The molecular weight of theepoxy-containing material may vary from 58 to about 100,000 or more.Mixtures of various epoxy-containing materials can also be used in thehot melt compositions of the invention. The "average" number of epoxygroups per molecule is defined as the number of epoxy groups in theepoxy-containing material divided by the total number of epoxy moleculespresent.

Useful epoxy-containing materials include those which containcyclohexene oxide groups such as the epoxycyclohexanecarboxylates,typified by 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate,3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methycyclohexanecarboxylate, and bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate. For amore detailed list of useful epoxides of this nature, reference may bemade to U.S. Pat. No. 3,117,099.

Further epoxy-containing materials which are particularly useful in thepractice of this invention include glycidyl ether monomers of theformula ##STR2## where R' is alkyl or aryl and n is an integer of 1 to6. Examples are the glycidyl ethers of polyhydric phenols obtained byreacting a polyhydric phenol with an excess of chlorohydrin such asepichlorohydrin (e.g., the diglycidyl ether of2,2-bis-(2,3-epoxypropoxyphenol) propane). Further examples of epoxidesof this type which can be used in the practice of this invention aredescribed in U.S. Pat. No. 3,018,262.

There is a host of commercially available epoxy-containing materialswhich can be used in this invention. In particular, epoxides which arereadily available include octadecylene oxide, epichlorohydrin, styreneoxide, vinyl cyclohexene oxide, glycidol, glycidylmethacrylate,diglycidyl ether of Bisphenol A (e.g., those available under the tradedesignations EPON 828, EPON 1004, and EPON 1001F from Shell ChemicalCo., and DER-332 and DER-334, from Dow Chemical Co.), diglycidyl etherof Bisphenol F (e.g., ARALDITE GY281 from Ciba-Geigy), vinylcyclohexenedioxide (e.g., ERL 4206 from Union Carbide Corp.),3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexene carboxylate (e.g.,ERL-4221 from Union Carbide Corp.),2-(3,4-epoxycylohexyl-5,5-spiro-3,4-epoxy) cyclohexane-metadioxane(e.g., ERL-4234 from Union Carbide Corp.), bis(3,4-epoxycyclohexyl)adipate (e.g., ERL-4299 from Union Carbide Corp.), dipentene dioxide(e.g., ERL-4269 from Union Carbide Corp.), epoxidized polybutadiene(e.g., OXIRON 2001 from FMC Corp.), silicone resin containing epoxyfunctionality, epoxy silanes (e.g.,beta-(3,4-epoxycyclohexyl)ethyltrimethoxy silane andgamma-glycidoxypropyltrimethoxy silane, commercially available fromUnion Carbide), flame retardant epoxy resins (e.g., DER-542, abrominated bisphenol type epoxy resin available from Dow Chemical Co.),1,4-butanediol diglycidyl ether (e.g., ARALDITE RD-2 from Ciba-Geigy),hydrogenated bisphenol A-epichlorohydrin based epoxy resins (e.g. EPONEX1510 from Shell Chemical Co.), and polyglycidyl ether ofphenolformaldehyde novolak (e.g., DEN-431 and DEN-438 from Dow ChemicalCo.).

Useful polyester components include both hydroxyl and carboxylterminated materials, which may be amorphous or semicrystalline.Hydroxyl terminated materials are preferred. By "amorphous" is meant amaterial that displays a glass transition temperature but does notdisplay a measurable crystalline melting point by differential scanningcalorimetry (DSC). Preferably the glass transition temperature is lessthan the decomposition temperature of the initiator (discussed below),but without being more than about 120° C. By "semicrystalline" is meanta polyester component that displays a crystalline melting point by DSC,preferably with a maximum melting point of about 150° C.

The viscosity of the polyester component is important in providing a hotmelt make coat (as opposed to a make coat which is a liquid having ameasurable viscosity at room temperature). Accordingly, polyestercomponents useful in the make coats of the invention preferably have aBrookfield viscosity which exceeds 10,000 milliPascals at 121° C.Viscosity is related to the molecular weight of the polyester component.Preferred polyester components also have a number average molecularweight of about 7500 to 200,000, more preferably from about 10,000 to50,000 and most preferably from about 15,000 to 30,000.

Polyester components useful in the make coats of the invention comprisethe reaction product of dicarboxylic acids (or their diesterderivatives) and diols. The diacids (or their diester derivatives) canbe saturated aliphatic acids containing from 4 to 12 carbon atoms(including unbranched, branched, or cyclic materials having 5 to 6 atomsin a ring) and/or aromatic acids containing from 8 to 15 carbon atoms.Examples of suitable aliphatic acids are succinic, glutaric, adipic,pimelic, suberic, azelaic, sebacic, 1,12 dodecanedioic,1,4-cyclohexanedicarboxylic, 1,3-cyclopentanedicarboxylic,2-methylsuccinic, 2-methylpentanedioic, 3-methylhexanedioic acids andthe like. Suitable aromatic acids include terephthalic acid, isophthalicacid, phthalic acid, 4,4'-benzophenone dicarboxylic acid,4,4'-diphenylmethanedicarboxylic acid, 4,4'-diphenylether dicarboxylicacid, 4,4'-diphenylthioether dicarboxylic acid and 4,4'-diphenylaminedicarboxylic acid. Preferably the structure between the two carboxylgroups in these diacids contains only carbon and hydrogen; morepreferably it is a phenylene group. Blends of any of the foregoingdiacids may be used.

The diols include branched, unbranched, and cyclic aliphatic diolshaving from 2 to 12 carbon atoms, such as, for example, ethylene glycol,1,3-propylene glycol, 1,2-propylene glycol, 1,4-butanediol,1,3-butanediol, 1,5-pentanediol, 2-methyl-2,4-pentanediol,1,6-hexanediol, 1,8-octanediol, cyclobutane-1,3-di(2'ethanol),cyclohexane-1,4-dimethanol, 1,10-decanediol, 1,12-dodecanediol, andneopentyl glycol. Long chain diols including poly(oxyalkylene) glycolsin which the alkylene group contains from 2 to 9 carbon atoms(preferably 2 to 4 carbon atoms) may also be used. Blends of any of theforegoing diols may be used.

Useful, commercially available hydroxyl terminated polyester materialsinclude various saturated, linear, semicrystalline copolyestersavailable from Huls America, Inc. such as DYNAPOL S1402, DYNAPOL S1358,DYNAPOL S1227, DYNAPOL S1229 and DYNAPOL S1401. Useful saturated, linearamorphous copolyesters available from Huls America, Inc. include DYNAPOLS1313 and DYNAPOL S1430.

The initiator functions to promote curing or covalent crosslinking ofthe hot melt make coat. The initiator may be activated byelectromagnetic radiation (e.g., light having a wavelength in theultraviolet or visible regions of the electromagnetic spectrum), byaccelerated particles (e.g., electron beam radiation), or thermally(e.g., heat or infrared radiation). Preferably, the initiators arephotoactive; that is, they are photoinitiators activated by actinicradiation (radiation having a wavelength in the ultraviolet or visibleportion of the electromagnetic spectrum).

Initiators which are useful in the make coats of the invention aregenerally of three types, viz. aromatic iodonium complex salts, aromaticsulfonium complex salts and metallocene salts. Preferably, these threetypes are selected to be photoinitiators.

Useful aromatic iodonium complex salts have the formula: ##STR3## whereAr¹ and Ar² are aromatic groups having 4 to 20 carbon atoms and areselected from the group consisting of phenyl, thienyl, furanyl andpyrazolyl groups. Z is selected from the group consisting of oxygen;sulfur; ##STR4## where R is aryl (of 6 to 20 carbons, such as phenyl) oracyl (of 2 to 20 carbons, such as acetyl, benzoyl, etc.); acarbon-to-carbon bond; or ##STR5## where R₁ and R₂ are selected fromhydrogen, alkyl radicals of 1 to 4 carbons, and alkenyl radicals of 2 to4 carbons. The value of m is zero or 1 and X is a halogen-containingcomplex anion selected from tetrafluoroborate, hexafluorophosphate,pentafluorohydroxyantimonate, hexafluoroarsenate, andhexafluoroantimonate.

The Ar¹ and Ar² aromatic groups may optionally have one or more fusedbenzo rings (e.g., naphthyl, benzothienyl, dibenzothienyl, benzofuranyl,dibenzofuranyl, etc.). The aromatic groups may also be substituted, ifdesired, by one or more non-basic groups if they are essentiallynon-reactive with epoxide and hydroxyl functionalities.

Useful aromatic iodonium complex salts are described more fully in U.S.Pat. No. 4,256,828. The preferred aromatic iodonium complex salts arediaryliodonium hexafluorophosphate and diaryliodoniumhexafluoroantimonate.

The aromatic iodonium complex salts useful in the make coats of theinvention are photosensitive only in the ultraviolet region of thespectrum. They, however, can be sensitized to the near ultraviolet andthe visible range of the spectrum by sensitizers for known photolyzableorganic halogen compounds. Illustrative sensitizers include aromaticamines and colored aromatic polycyclic hydrocarbons.

Aromatic sulfonium complex salt initiators suitable for use in the makecoats of the invention can be defined by the formula ##STR6## whereinR₃, R₄ and R₅ can be the same or different, provided that at least oneof the groups is aromatic. These groups can be selected from aromaticmoieties having 4 to 20 carbon atoms (e.g., substituted andunsubstituted phenyl, thienyl, and furanyl) and alkyl radicals having 1to 20 carbon atoms. The term "alkyl" includes substituted alkyl radicals(for example, substituents such as halogen, hydroxy, alkoxy, aryl).Preferably, R₃, R₄ and R₅ are each aromatic. Z, m and X are all asdefined above with regard to the iodonium complex salts.

If R₃, R₄ or R₅ is an aromatic group, it may optionally have one or morefused benzo rings (e.g, naphthyl, benzothienyl, dibenzothienyl,benzofuranyl, dibenzofuranyl, etc.) Such aromatic groups may also besubstituted, if desired, by one or more non-basic groups that areessentially non-reactive with epoxide and hydroxyl functionality.

The triaryl-substituted salts such as triphenylsulfoniumhexafluoroantimonate are the preferred sulfonium salts. Useful sulfoniumcomplex salts are described more fully in U.S. Pat. No. 4,256,828.

The aromatic sulfonium complex salts useful in the invention areinherently photosensitive only in the ultraviolet region of thespectrum. They, however, are sensitized to the near ultraviolet and thevisible range of the spectrum by a select group of sensitizers such asdescribed in U.S. Pat. No. 4,256,828.

Useful metallocene salts can have the formula:

    [(L.sup.1)(L.sup.2)M.sup.p ]+.sup.q Y.sub.r

wherein:

M^(p) represents a metal selected from Cr, Mo, W, Mn, Re, Fe, and Co;

L¹ represents 1 or 2 ligands contributing π-electrons that can be thesame or different ligand selected from substituted and unsubstituted η³-allyl, η⁵ -cyclopentadienyl, and η⁷ -cycloheptatrienyl and η⁶ -aromaticcompounds selected from η⁶ -benzene and substituted η⁶ -benzenecompounds and compounds having 2 to 4 fused rings each capable ofcontributing 3 to 8 π-electrons to the valence shell of M^(p) ;

L² represents none or 1 to 3 ligands contributing an even number ofsigma-electrons that can be the same or different ligand selected fromcarbon monoxide or nitrosonium;

with the proviso that the total electronic charge contributed to M^(p)by L¹ and L² plus the ionic charge on the metal M^(p) results in a netresidual positive charge of q to the complex, and

q is an integer having a value of 1 or 2, the residual electrical chargeof the complex cation;

Y is a halogen-containing complex anion selected from AsF₆ --, SbF₆ --and SbF₅ OH--; and

r is an integer having a value of 1 or 2, the numbers of complex anionsrequired to neutralize the charge q on the complex cation.

Useful metallocene salts are described more fully in U.S. Pat. No.5,089,536. It is desirable for the metallocene salt initiators to beaccompanied by an accelerator such as an oxalate ester of a tertiaryalcohol, although this is optional. The accelerator preferably comprisesfrom about 0.1 to 4% of the make coat based on the combined weight ofthe epoxy-containing material and the polyester component, morepreferably about 60% of the weight of the metallocene initiator.

Useful commercially available initiators include FX-512, an aromaticsulfonium complex salt (3M Company), UVI-6974, an aromatic sulfoniumcomplex salt (Union Carbide Corp.),and IRGACURE 261, a metallocenecomplex salt (Ciba-Geigy).

Optionally, the hot melt make coats of the invention may furthercomprise a hydroxyl-containing material. The hydroxyl-containingmaterial may be any liquid or solid organic material having hydroxylfunctionality of at least 1, preferably at least 2, and most preferablyabout 3. The hydroxyl-containing organic material should be free ofother "active hydrogen" containing groups such as amino and mercaptomoieties. The hydroxyl-containing organic material should also besubstantially free of groups which may be thermally or photolyticallyunstable so that the material will not decompose or liberate volatilecomponents at temperatures below about 100° C. or when exposed to theenergy source during curing. Preferably the organic material containstwo or more primary or secondary aliphatic hydroxyl groups (i.e., thehydroxyl group is bonded directly to a nonaromatic carbon atom). Thehydroxyl group may be terminally situated, or may be pendent from apolymer or copolymer. The number average equivalent weight of thehydroxyl-containing material is preferably about 31 to 2250, morepreferably about 80 to 1000, and most preferably about 80 to 350.

Representative examples of suitable organic materials having a hydroxylfunctionality of 1 include alkanols, monoalkyl ethers of polyoxyalkyleneglycols, and monoalkyl ethers of alkylene glycols.

Representative examples of useful monomeric polyhydroxy organicmaterials include alkylene glycols (e.g., 1,2-ethanediol,1,3-propanediol, 1,4-butanediol, 2-ethyl-1,6-hexanediol, 1,4 cyclohexanedimethanol, 1,18-dihydroxyoctadecane, and 3-chloro-1,2-propanediol),polyhydroxyalkanes (e.g., glycerine, trimethylolethane, pentaerythritol,and sorbitol) and other polyhydroxy compounds such asN,N-bis(hydroxyethyl)benzamide, 2-butene-1,4-diol, castor oil, etc.

Representative examples of useful polymeric hydroxyl-containingmaterials include polyoxyalkylene polyols (e.g., polyoxyethylene andpolyoxypropylene glycols and triols of equivalent weight of 31 to 2250for the diols or 80 to 350 for triols), polytetramethylene oxide glycolsof varying molecular weight, hydroxyl-terminated polyesters, andhydroxyl-terminated polylactones.

Useful commercially available hydroxyl-containing materials include thePOLYMEG series (available from QO Chemicals, Inc.) of polytetramethyleneoxide glycols such as POLYMEG 650, 1000 and 2000; the TERATHANE series(from E. I. dupont de Nemours and Company) of polytetramethylene oxideglycols such as TERATHANE 650, 1000 and 2000; POLYTHF, apolytetramethylene oxide glycol from BASF Corp.; the BUTVAR series(available from Monsanto Chemical Company) of polyvinylacetal resinssuch as BUTVAR B-72A, B-73, B-76, B-90 and B-98; the TONE series(available from Union Carbide) of polycaprolactone polyols such as TONE0200, 0210, 0230, 0240, and 0260; the DESMOPHEN series (available fromMiles Inc.) of saturated polyester polyols such as DESMOPHEN 2000, 2500,2501, 2001KS, 2502, 2505, 1700, 1800, and 2504; the RUCOFLEX series(available from Ruco Corp.) of saturated polyester polyols such asS-107, S-109, S-1011 and S-1014; VORANOL 234-630 (a trimethylol propane)from Dow Chemical Company; VORANOL 230-238 (a glycerol polypropyleneoxide adduct) from Dow Chemical Company; the SYNFAC series (fromMilliken Chemical) of polyoxyalkylated bisphenol A's such as SYNFAC8009, 773240, 8024, 8027, 8026, and 8031; and the ARCOL series (fromArco Chemical Co.) of polyoxypropylene polyols such as ARCOL 425, 1025,2025, 42, 112, 168, and 240.

The amount of hydroxyl-containing organic material used in the makecoats of the invention may vary over a broad range, depending on factorssuch as the compatibility of the hydroxyl-containing material with boththe epoxy-containing material and the polyester component, theequivalent weight and functionality of the hydroxyl-containing material,and the physical properties desired in the final cured make coat.

The optional hydroxyl-containing material is particularly useful intailoring the flexibility of the hot melt make coats of the invention.As the equivalent weight of the hydroxyl-containing material increases,the flexibility of the hot melt make coat correspondingly increasesalthough there may be a consequent loss in cohesive strength. Similarly,decreasing equivalent weight may result in a loss of flexibility with aconsequent increase in cohesive strength. Thus, the equivalent weight ofthe hydroxyl-containing material is selected so as to balance these twoproperties.

If the hydroxyl-containing material is used to tailor the flexibility ofthe hot melt make coat, polyoxyethylene glycols and triols having anequivalent weight of about 31 to 2250 for the glycols and 80 to 350 forthe triols are particularly preferred. Even more preferred arepolyoxypropylene glycols and triols having a hydroxyl functionalitygreater than 2 and an equivalent weight of about 31 to 2250 for theglycols and 80 to 350 for the triols. Polyoxyalkylene polyols are mostadvantageously employed when the initiator is either an aromaticiodonium complex salt or an aromatic sulfonium complex salt. Ifmetallocene salts are used as the initiator, 1,4 cyclohexanedimethanolis a particularly preferred flexiblizer.

As explained more fully hereinbelow, the incorporation of polyetherpolyols into the hot melt make coats of the invention is especiallydesirable for adjusting the rate at which the make coats cure uponexposure to energy. Useful polyether polyols (i.e., polyoxyalkylenepolyols) for adjusting the rate of cure include polyoxyethylene andpolyoxypropylene glycols and triols having an equivalent weight of about31 to 2250 for the diols and about 80 to 350 for the triols, as well aspolytetramethylene oxide glycols of varying molecular weight andpolyoxyalkylated bisphenol A's. Polyether polyols as cure inhibitors arebest used in conjunction with aromatic iodonium complex salts andaromatic sulfonium complex salts. Metallocene salt initiators inherentlyprovide a delayed cure which need not be further retarded by theinclusion of a polyether polyol.

The hot melt make coats of the invention comprise from 2 to 95 parts per100 parts total of the epoxy-containing material and, correspondingly,from 98 to 5 parts of the polyester component. More preferably, the hotmelt make coats of the invention comprise from 2 to 80 parts of theepoxy-containing material and, correspondingly, from 98 to 20 parts ofthe polyester component. Increasing amounts of the epoxy-containingmaterial relative to the polyester component tend to result in stiffermake coats. Thus, the relative amounts of these two ingredients arebalanced depending on the properties sought in the final make coat.

The initiator is included in an amount ranging from about 0.1 to 4%based on the combined weight of the epoxy-containing material and thepolyester component. Increasing amounts of the initiator result in anaccelerated curing rate but require that the hot melt make coat beapplied in a thinner layer so as to avoid curing only at the surface.Increased amounts of initiator can also result in reduced energyexposure requirements and a shortened pot life at applicationtemperatures. The amount of the initiator is determined by the rate atwhich the make coat should cure, the intensity of the energy source, andthe thickness of the make coat.

The relative amount of the optional hydroxyl-containing organic materialis determined with reference to the ratio of the number of hydroxylgroups to the number of epoxy groups in the hot melt make coat. Thatratio may range from 0:1 to 1:1, more preferably from about 0.4:1 to0.8:1. Larger amounts of the hydroxyl-containing material increase theflexibility of the hot melt make coat but with a consequent loss ofcohesive strength. If the hydroxyl containing material is a polyetherpolyol, increasing amounts will further slow the curing process.

Size coat 20 is applied over abrasive particles 16 and make coat 18. Thesize coat may comprise a glue or a cured resinous adhesive. Examples ofsuitable resinous adhesives include phenolic, aminoplast, urethane,acrylated urethane, epoxy, acrylated epoxy, isocyanurate, acrylatedisocyanurate, ethylenically unsaturated, urea-formaldehyde,bis-maleimide and fluorene-modified epoxy resins as well as mixturesthereof. Precursors for the size coat may further include catalystsand/or curing agents to initiate and/or accelerate the curing processdescribed hereinbelow. The size coat is selected based on the desiredcharacteristics of the finished coated abrasive article.

Both the make and size coats may additionally comprise various optionaladditives such as fillers, grinding aids, fibers, lubricants, wettingagents, surfactants, pigments, antifoaming agents, dyes, couplingagents, plasticizers and suspending agents so long as they do notadversely affect the pressure sensitive adhesive properties of the makecoat (before it fully cures) or detrimentally effect the ability of themake coat to cure upon exposure to energy. Examples of useful fillersinclude calcium carbonate, calcium metasilicate, silica, silicates,sulfate salts and combinations thereof. Grinding aids useful in thepractice of the invention include cryolite, ammonium cryolite andpotassium tetrafluoroborate.

Abrasive layer 14 may further comprise a third binder or super sizecoating 22. One useful super size coating comprises a grinding aid, suchas potassium tetrafluoroborate, and an adhesive, such as an epoxy resin.Super size coating 22 may be included to prevent or reduce theaccumulation of swarf (the material abraded from a workpiece) betweenabrasive particles which can dramatically reduce the cutting ability ofthe abrasive article. Materials useful in preventing swarf accumulationinclude metal salts of fatty acids (e.g., zinc stearate),urea-formaldehydes, waxes, mineral oils, crosslinked silanes,crosslinked silicones, fluorochemicals and combinations thereof.

An optional back size coating 24 such as an antislip layer comprising aresinous adhesive having filler particles dispersed therein or apressure sensitive adhesive for bonding the coated abrasive article to asupport pad may be provided on backing 12. Examples of suitable pressuresensitive adhesives include latex, crepe, rosin, acrylate polymers(e.g., polybutyl acrylate and polyacrylate esters), acrylate copolymers(e.g., isooctylacrylate/acrylic acid), vinyl ethers (e.g., polyvinyln-butyl ether), alkyd adhesives, rubber adhesives (e.g., naturalrubbers, synthetic rubbers and chlorinated rubbers), and mixturesthereof.

The back size coating may also be an electrically conductive materialsuch as vanadium pentoxide (in, for example, a sulfonated polyester), orcarbon black or graphite in a binder. Examples of useful conductive backsize coatings are disclosed in U.S. Pat. No. 5,108,463 and U.S. Pat. No.5,137,452, which patents are incorporated herein by reference.

In order to promote the adhesion of make coat 18 and/or back sizecoating 24 (if such be included), it may be necessary to modify thesurface to which these layers are applied. Appropriate surfacemodifications include corona discharge, ultraviolet light exposure,electron beam exposure, flame discharge and scuffing.

Alternatively, although not shown specifically in the drawings, abrasivelayer 14 may comprise a multiplicity of abrasive particles which aredispersed in the make coat. Such structures may further comprise anoptional super size coating, such as described above, over the makecoat. Both the construction illustrated in FIG. 2 and one in which theabrasive particles are dispersed in a make coat are considered exemplaryof abrasive layers comprising abrasive particles in a make coat or afirst binder.

Coated abrasive articles according to the invention may be made byapplying abrasive layer 14 to a preformed backing 12. The hot melt makecoat is prepared by mixing the various ingredients in a suitable vessel,preferably one that is not transparent to actinic radiation, at anelevated temperature sufficient to liquify the materials so that theymay be efficiently mixed but without thermally degrading them (e.g., atemperature of about 120° C.) with stirring until the components arethoroughly melt blended. The components may be added simultaneously orsequentially, although it is preferred to first blend theepoxy-containing material and the polyester component followed by theaddition of the hydroxyl-containing material and then the initiator.

The hot melt make coat should be compatible in the melt phase. That is,there should be no visible gross phase separation among the components.The make coat may be used directly after melt blending or may bepackaged as a solvent free system in pails, drums or other suitablecontainers, preferably in the absence of light, until ready for use. Themake coats so packaged may be delivered to a hot-melt applicator systemwith the use of pail unloaders and the like. Alternatively, the hot meltmake coats of the invention may be delivered to conventional bulk hotmelt applicator and dispenser systems in the form of sticks, pellets,slugs, blocks, pillows or billets.

It is also possible to provide the hot melt make coats of the inventionas uncured, unsupported rolls of tacky, pressure sensitive adhesivefilm. Such films are useful in laminating the make coat to an abrasivearticle backing. It is desirable to roll the tacky film up with arelease liner (for example, silicone-coated Kraft paper), withsubsequent packaging in a bag or other container that is not transparentto actinic radiation.

The hot melt make coats of the invention may be applied to the abrasivearticle backing by extruding, gravure printing, or coating, (e.g., byusing a coating die, a heated knife blade coater, a roll coater, acurtain coater, or a reverse roll coater). When applying by any of thesemethods, it is preferred that the make coat be applied at a temperatureof about 100° to 125° C., more preferably from about 80° to 125 ° C.Coating is a desirable application method for use with J weight clothbackings and other fabric backings of similar porosity.

The hot melt make coats can be supplied as free standing, unsupportedpressure sensitive adhesive films that can be laminated to the backingand, if necessary, die cut to a predefined shape before lamination.Lamination temperatures and pressures are selected so as to minimizedegradation of the backing and bleed through of the make coat and mayrange from room temperature to about 120° C. and about 30 to 250 psi. Atypical profile is to laminate at room temperature and 100 psi.Lamination is a particularly preferred application method for use withhighly porous backings; for example, backings which are more porous thanstandard J weight cloth.

Preferably, the hot melt make coat is applied to the abrasive articlebacking by any of the methods described above, and once so applied isexposed to an energy source to initiate the curing of theepoxy-containing material. The epoxy-containing material is believed tocure or crosslink with itself, the optional hydroxyl-containingmaterial, and, perhaps, to some degree with the polyester component.

Curing of the hot melt make coat begins upon exposure of the make coatto any energy-producing source and continues for a period of timethereafter. The energy may be electromagnetic (e.g., radiation having awavelength in the ultraviolet or visible region of the spectrum),accelerated particles (e.g., electron beam radiation), or thermal (e.g.,heat or infrared radiation). Preferably, the energy is actinic radiation(i.e., radiation having a wavelength in the ultraviolet or visiblespectral regions). Suitable sources of actinic radiation includemercury, xenon, carbon arc, tungsten filament lamps, sunlight, etc.Ultraviolet radiation, especially from a medium pressure mercury arclamp, is most preferred. Exposure times may be from less than about 1second to 10 minutes or more (to provide a total energy exposure ofabout 1.0 Joule/square centimeter (J/cm²)) depending upon both theamount and the type of reactants involved, the energy source, thedistance from the energy source, and the thickness of the make coat tobe cured.

The make coats may also be cured by exposure to electron beam radiation.The dosage necessary is generally from less than 1 megarad to 100megarads or more. The rate of curing tends to increase with increasingamounts of initiator at a given energy exposure. The rate of curing alsoincreases with increased energy intensity.

Those hot melt make coats which include a polyether polyol that retardsthe curing rate are particularly desirable because the delayed cureenables the make coat to retain its pressure sensitive properties for atime sufficient to permit abrasive particles to be adhered thereto afterthe make coat has been exposed to the energy source. (A similar effectis possible by using a metallocene salt initiator without a polyetherpolyol.) The abrasive particles may be applied until the make coat hassufficiently cured that the particles will no longer adhere, although toincrease the speed of a commercial manufacturing operation it isdesirable to apply the abrasive particles as soon as possible, typicallywithin a few seconds of the make coat having been exposed to the energysource. Thus it will be recognized that the polyether polyol can providethe hot melt make coats with an open time. That is, for a period of time(the open time) after the make coat has been exposed to the energysource, it remains sufficiently tacky and uncured for the abrasiveparticles to be adhered thereto. The abrasive particles are projectedinto the make coat by any suitable method, preferably by electrostaticcoating.

The time to reach full cure may be accelerated by post curing the makecoat with heat, such as in an oven. Post curing can also affect thephysical properties of the make coat and is generally desirable. Thetime and temperature of the post cure will vary depending upon the glasstransition temperature of the polyester component, the concentration ofthe initiator, the energy exposure conditions, and the like. Post cureconditions can range from less than 1 minute at a temperature of about150° C. to longer times at lower temperatures. Typical post cureconditions are about 2 minutes at a temperature of about 80° C.

In an alternative manufacturing approach, the make coat is applied tothe backing and the abrasive particles are then projected into the makecoat followed by exposure of the make coat to an energy source. Whilethe total energy requirements for curing the make coat in this processare about the same as in the process in which the make coat is exposedto energy before the abrasive particles are applied, the use of lessintense energy for a longer period of time is preferred. Thermal postcuring is not generally required in the practice of this alternativemethod.

If the abrasive layer comprises a dispersion of abrasive particles in amake coat, an abrasive slurry comprising the particles and the make coatis prepared and coated onto the backing by roll coating, dip coating,knife coating, and the like. The make coat may then be cured by theprocesses described above.

Size coat 20 may be subsequently applied over the abrasive particles andthe make coat as a flowable liquid by a variety of techniques such asroll coating, spray coating or curtain coating and can be subsequentlycured by drying, heating, or with electron beam or ultraviolet lightradiation. The particular curing approach may vary depending on thechemistry of the size coat. Optional super size coating 22 may beapplied and cured in a similar manner.

Optional back size coating 24 may be applied to backing 12 using any ofa variety of conventional coating techniques such as dip coating, rollcoating, spraying, Meyer bar, doctor blade, gravure printing, thermomasstransfer, flexographic printing, screen printing, and the like.

The make coats of the invention provide a unique balance of highlydesirable properties. As solvent free formulations, they are easilyapplied using conventional hot melt dispensing systems. Consequently,they can be supplied as pressure sensitive adhesive films well suitedfor lamination to a backing. The inclusion of a polyester componentprovides the make coats with pressure sensitive properties whichfacilitates the application of the abrasive particles thereto. Theprovision of a polyether polyol of appropriate molecular weight andfunctionality provides the make coats of the invention with an open timesubsequent to energy exposure that permits the abrasive particles to beprojected into the make coat after it has been exposed to energy.However, the hot melt composition cures to yield a tough, durableaggressively bonded crosslinked, thermoset make coat.

The invention will be more fully understood with reference to thefollowing nonlimiting examples in which all parts refer to parts byweight. Abbreviations used in the examples have the definitions shown inthe following schedule.

    ______________________________________                                        DYNAPOL     A high molecular weight polyester                                 S1402       with low crystallinity. (Commercially                                         available from Huls America.)                                     EPON 828    A bisphenol A epoxy resin having an                                           epoxy equivalent weight of about 185-                                         192 grams/equivalent. (Commercially                                           available from Shell Chemical.)                                   EPON 1001F  A bisphenol A epoxy resin having an                                           epoxy equivalent weight of about 525-                                         550 grams/equivalent. (Commercially                                           available from Shell Chemical.)                                   tBOX        di-t-butyl oxalate, an accelerator.                               CHDM        cyclohexanedimethanol, a hydroxyl-                                            containing material.                                              VORANOL     A polyol adduct of glycerol and                                   230-238     propylene oxide having a hydroxyl                                             number of 38. (Commercially available                                         from Dow Chemical Company.)                                       COM         eta.sup.6 -[xylenes (mixed isomers)]eta.sup.5 -                               cyclopentadienyliron(1+)                                                      hexafluoroantimonate, an initiator.                               AMOX        di-t-amyloxalate, an accelerator.                                 TSA         Triphenyl sulfonium                                                           hexafluoroantimonate, an initiator.                               BORDEN      A urea-formaldehyde resin.                                        8505        (Commercially available from Borden,                                          Inc.)                                                             ______________________________________                                    

EXAMPLE 1

The coated abrasive article of example 1 included a J weight cottonbacking that had been wet and stretched but not sealed. A make coatcomprising DYNAPOL S1402 (40.4 parts), EPON 828 (29.3 parts), EPON 1001F(29.9 parts), CHDM (2.4 parts), COM (1.0 part), and AMOX (0.6 part) wasprepared by preheating the EPON 828, the EPON 1001F, and the DYNAPOLS1402 in a suitable reaction vessel at 121° C. for 30 minutes. The CHDMwas then added with mixing at 121° C. for 3 hours until a homogeneousmelt blend was obtained. The temperature was then reduced to 100° C. andthe AMOX and the COM were added with stirring at 100° C. for one hour.

The make coat was applied at 125° C. with a die coater to the front sideof the backing at a weight of about 84 grams/square meter (g/m²). Themake coat (on the backing) was exposed to a UVXL 200/300/400 watts/inchthree-setting type "D" ultraviolet lamp (available from AetekInternational, Inc. (Plainfield, Ill.), running on its 200 watts perinch setting with a web feed rate of 0.10 meter/second so as to providea total energy exposure of about 50 to 60 milliJoules/cm². The make coatwas exposed to the ultraviolet radiation immediately before grade 80fused aluminum oxide abrasive particles were electrostatically projectedinto the make coat at a weight of about 327 g/m². The resulting productwas then post cured for 30 minutes at 80° C.

A 60% solids size coat comprising BORDEN 8405 (6500 parts), feldspar(2100 parts), aluminum chloride (452 parts, 10% solids in water), andwater (948 parts) was roll coated over the abrasive particles at a wetweight of about 159 g/m². The resulting article was heated for 45minutes at 66° C. and then flexed before testing.

EXAMPLE 2

Example 2 was prepared according to the procedure described in example 1except that the make coat was applied at a weight of about 126 g/m².

Comparative Examples 1 and 2

Two comparative examples using commercially available coated abrasivearticles were also provided. Comparative example (C.E.) 1 was a grade 803M 211 ELEK-TRO-CUT coated abrasive article having a J weight clothbacking and commercially available from 3M Company. Comparative example2 was a grade 80 3M 311T BLUE GRIT coated abrasive article having a Jweight cloth backing, also commercially available from 3M Company.

EXAMPLE 3

A make coat comprising DYNAPOL S1402 (40.0 parts), EPON 828 (15.0parts), EPON 1001F (29.0 parts), VORANOL 230-238 (15.0 parts), and TSA(1.0 part) was prepared by blending those materials in a suitable vesselfor 15 minutes at 121° C. until the ingredients were melt blendedfollowed by an additional 5 minutes of mixing. The make coat was appliedto a backing like that used in example 1 at 125° C. with a heated knifeand at a weight of about 49 g/m². Grade 120 aluminum oxide abrasiveparticles were drop coated into the make coat at a weight of about 209g/m². The resulting product was immediately exposed to a bank ofF15T8350BL (Sylvania Corp.) low intensity ultraviolet radiation lampsfrom the mineral side (1000 milliJoules/cm² at a web feed rate of 0.51centimeter/second for 10 minutes) in a nitrogen environment. The sizecoat of example 1 was then roll coated over the abrasive particles at awet weight of about 109 g/m².

EXAMPLE 4

Example 4 was prepared according to the procedure of example 3 exceptthat the make coat was applied at a weight of about 123 g/m². Examples 3and 4 demonstrate that the make coat can be energy cured after theabrasive particles have been applied.

Comparative Example 3

Comparative example 3 was a grade 120 3M 311T BLUE GRIT coated abrasivearticle having a J weight utility cloth backing, commercially availablefrom 3M Company.

EXAMPLE 5

A make coat was prepared according to the procedure described in example1 and coated at 125° C. with a heated knife coater between twoapproximately 102 μm thick release liners at a weight of about 84 g/m²so as to provide a free standing tacky, pressure sensitive adhesivefilm. One release liner was removed and the exposed face of the adhesivefilm was laminated to a cotton backing like that used in example 1 at apressure of about 690 kiloPascals and at room temperature (about 20° to22° C.). The make coat was irradiated as described in example 1. Theresulting article was then coated with abrasive particles, thermallypost cured, provided with a size coat, heated and flexed, all asdescribed in example 1. Example 5 demonstrates that the make coats usedin coated abrasive articles according to the invention can be providedas free standing, tacky pressure sensitive adhesive films that can belaminated to a porous cloth backing.

Examples 1 to 5 and comparative examples 1 to 3 were tested according tosome or all of the following procedures.

Test Procedures

90° Peel Test.

To measure the adhesion between the backing and the make coat, thecoated abrasive article of several of the examples and comparativeexamples was converted into a sample about 8 cm wide by 25 cm long.One-half the length of a wooden board (17.78 cm long by 7.62 wide cm by0.64 cm thick) was coated with JET-MELT 3779-PG adhesive commerciallyavailable from 3M Company. The entire width of, but only the first 15 cmof the length of, the coated abrasive article was coated on its abrasiveparticle side with the same adhesive. The side of the article bearingthe abrasive particles and the adhesive was attached to the side of theboard containing adhesive such that the 10 cm portion of the coatedabrasive article not bearing adhesive overhung the board. Pressure wasapplied to intimately bond the board and the article. The test set-upwas constructed in a manner that ensured that separation during the testwould occur between layers of the coated abrasive article rather thanbetween the coated abrasive article and the wooden board.

The abrasive article was then scored in a straight line such that itswidth was reduced to 5.1 cm. The resulting coated abrasivearticle/wooden board composite was mounted horizontally in the lower jawof a SINTECH tensile testing machine with approximately 1 cm of theoverhanging portion of the coated abrasive article mounted in the upperjaw. The distance between the jaws was 12.7 cm and the separation ratewas 0.5 cm/sec with the coated abrasive article being pulled away fromthe wooden board at an angle of 90° so as to separate the make coat fromthe cloth backing. The separation force was recorded in kilograms percentimeter of article width (kg/cm), larger values indicating betteradhesion between the make coat and the cloth backing. Preferably theseparation force is at least 1.8 kg/cm, more preferably at least 2kg/cm. The results are reported below in Table 1.

Disc Test.

The disc test was used to evaluate the ability of a coated abrasivearticle to abrade a polymeric workpiece, with the results shown below inTable 1. More specifically, the coated abrasive articles of examples 1and 2 and comparative examples 1 and 2 were die cut to provide 10.2 cmdiameter discs that were bonded to a foam back-up pad with a pressuresensitive adhesive. The coated abrasive disc and foam back-up pad weremounted in a Schiefer testing apparatus to dry abrade apolymethylmethacrylate workpiece for 500 revolutions under a 4.5 kgload. The workpiece was a disc having an opening through a centralportion thereof. The outside diameter of the disc was 10.2 cm and theinside diameter was 5.1 cm. The amount of abraded polymer in grams (g)was weighed. The surface finish of the abraded workpiece was assessed bymeasuring R_(a) (the arithmetic average of the scratch depth inmicroinches (μin)). The weight of abraded polymer should be at leastabout 1.3 g.

Rocker Drum Test.

A rocker drum test was used to evaluate the. ability of a coatedabrasive article to abrade a metal workpiece. More specifically, thecoated abrasive articles of examples 3 and 4 and comparative examples 1and 2 were converted into 10.2 cm wide by 15.2 cm long sheets that weremounted to the cylindrical drum of rocker drum testing machine whichoscillated (rocked) back and forth at the rate of about 60 strokes perminute (one complete back and forth cycle equalling one stroke). Theoscillatory motion against a stationery 1.3 cm wide by 15.2 cm long by1.3 cm thick Type 3008F aluminum workpiece wore an approximately 1.3 cmwide by 14.0 cm long path on the coated abrasive article. The forceapplied to the workpiece was 2.7 kg. The weight of the abraded aluminumin grams (g) was measured with the results shown below in Table 1. Thenumber following the slash in the table indicates the number of cyclesto which the test piece was subjected.

                  TABLE 1                                                         ______________________________________                                                90° Peel                                                                       Material Abraded(g)                                                     Force    Disc      Rocker  Ra                                       Example   (kg/cm)  Test      Drum Test                                                                             (μin)                                 ______________________________________                                        1         2.0      1.37      N.T.    97                                       2         2.0      1.28       0.17/62                                                                              90                                       C.E.1     N.T.     1.31      N.T.    113                                      C.E.2     2.0      1.32      0.98/402                                                                              105                                      3         2.3      N.T.      0.31/100                                                                              N.T.                                     4         2.9      N.T.      0.31/100                                                                              N.T.                                     C.E.3     N.T.     N.T.      0.32/100                                                                              N.T.                                     5         2.1      1.64      0.83/320                                                                              N.T.                                     ______________________________________                                         N.T. = Not tested.                                                       

The data of Table 1 show that examples 1 and 2, as compared tocomparative examples 1 and 2, performed similarly in the peel force anddisc tests with a slightly finer finish but without the need for asaturant coat or the like on the backing. Examples 3 and 4, as comparedto comparative example 3, indicate that even without a saturant coat orthe like on the backing, these coated abrasive articles performedsimilarly to a commercially available coated abrasive article.

Numerous modifications and variations are possible within the scope ofthe foregoing specification and drawings without departing from theinvention which is defined in the accompanying claims.

We claim:
 1. A method of preparing a coated abrasive article, the methodcomprising the steps of:(a) providing a backing; (b) hot melt applyingto the backing a curable hot melt adhesive first binder that comprisesan epoxy-containing material and a hydroxyl-terminated polyestercomponent; (c) exposing the first binder to an energy-producing sourceto initiate curing of the first binder; (d) depositing a plurality ofabrasive particles in the first binder; and (e) permitting the firstbinder to cure to a crosslinked coating with the abrasive particlestherein.
 2. A method of preparing a coated abrasive article according toclaim 1 wherein the backing is a porous cloth, textile or fabricmaterial.
 3. A method of preparing a coated abrasive article accordingto claim 1 wherein the first binder is exposed to actinic radiation instep (c).
 4. A method of preparing a coated abrasive article accordingto claim 1 wherein the abrasive particles are deposited in the firstbinder after the first binder has been exposed to the energy-producingsource.
 5. A method of preparing a coated abrasive article according toclaim 4 wherein the first binder has pressure sensitive properties whenthe abrasive particles are deposited therein.
 6. A method of preparing acoated abrasive article according to claim 5 comprising the additionalstep of thermally post-curing the first binder after it has been exposedto the energy-producing source and the abrasive particles have beendeposited therein.
 7. A method of preparing a coated abrasive articleaccording to claim 1 wherein the polyester component has a numberaverage molecular weight of 15,000-200,000.
 8. A method of preparing acoated abrasive article according to claim 1 wherein the first binder isthe reaction product of the epoxy-containing material, thehydroxyl-terminated polyester component, and a hydroxyl-containingmaterial.
 9. A method of preparing a coated abrasive article accordingto claim 1 wherein the first binder is hot melt applied to the backingat a temperature of at least about 80° C.
 10. A method of preparing acoated abrasive article according to claim 1 wherein the first binder isthe reaction product of the epoxy-containing material and thehydroxyl-terminated polyester component.
 11. A method of preparing acoated abrasive article according to claim 1 wherein the first binderfurther includes a photointiator for curing the first binder.
 12. Amethod of preparing a coated abrasive article, the method comprising thesteps of:(a) providing a backing; (b) applying to the backing a curablefirst binder that comprises:(1) an epoxy-containing material and ahydroxyl-terminated polyester component; and (2) a photoinitiator forcuring the first binder; (c) exposing the first binder to actinicradiation to initiate curing of the first binder; (d) depositing aplurality of abrasive particles in the first binder; and (e) permittingthe first binder to cure to a crosslinked coating with the abrasiveparticles therein.
 13. A method of preparing a coated abrasive articleaccording to claim 12 wherein the backing is a porous cloth, textile orfabric material.
 14. A method of preparing a coated abrasive articleaccording to claim 12 wherein the abrasive particles are deposited inthe first binder after the first binder has been exposed to actinicradiation.
 15. A method of preparing a coated abrasive article accordingto claim 14 wherein the first binder has pressure sensitive propertieswhen the abrasive particles are deposited therein.
 16. A method ofpreparing a coated abrasive article according to claim 15 comprising theadditional step of thermally post-curing the first binder after thefirst binder has been exposed to actinic radiation and the abrasiveparticles have been deposited therein.
 17. A method of preparing acoated abrasive article according to claim 12 wherein the abrasiveparticles are deposited in the first binder before the first binder isexposed to actinic radiation.
 18. A method of preparing a coatedabrasive article according to claim 12 wherein the first binder is thereaction product of the epoxy-containing malarial and thehydroxyl-terminated polyester component.
 19. A method of preparing acoated abrasive article, the method comprising the steps of:(a)providing a backing; (b) applying to the backing a curable first binderthat comprises an epoxy-containing material and a hydroxyl-terminatedpolyester component; (c) exposing the first binder to radiation selectedfrom the group consisting of electromagnetic radiation and acceleratedparticle radiation to initiate curing of the first binder; (d)depositing a plurality of abrasive particles in the first binder; and(e) permitting the first binder to cure to a crosslinked coating withthe abrasive particles therein.
 20. A method of preparing a coatedabrasive article according to claim 19 wherein the backing is a porouscloth, textile or fabric material.
 21. A method of preparing a coatedabrasive article according to claim 19 wherein the first binder isexposed to ultraviolet radiation in step (c).
 22. A method of preparinga coated abrasive article according to claim 19 wherein the first binderis exposed to electron beam radiation in step (c).
 23. A method ofpreparing a coated abrasive article according to claim 19 wherein theabrasive particles are deposited in the first binder alter the firstbinder has been exposed to radiation.
 24. A method of preparing a coatedabrasive article according to claim 23 wherein the first binder haspressure sensitive properties when the abrasive particles are depositedtherein.
 25. A method of preparing a coated abrasive article accordingto claim 24 comprising the additional step of thermally post-curing thefirst binder after it has been exposed to radiation and the abrasiveparticles have been deposited therein.
 26. A method of preparing acoated abrasive article according to claim 19 wherein the first binderis the reaction product of the epoxy-containing material and thehydroxyl-terminated polyester component.
 27. A method of preparing acoated abrasive article according to claim 19 wherein the first binderfurther includes a photointiator for curing the first binder.
 28. Amethod of preparing a coated abrasive article, the method comprising thesteps of:(a) providing a backing; (b) hot melt coating the backing witha curable hot melt adhesive first binder that comprises:(1) anepoxy-containing material and a hydroxyl-terminated polyester component;and (2) a photoinitiator for curing the first binder; (c) exposing thefirst binder to actinic radiation to initiate curing of the firstbinder; (d) depositing a plurality of abrasive particles in the firstbinder; (e) thermally post-curing the first binder to a crosslinkedcoating with the abrasive particles therein; (f) applying a curablesecond binder over the first binder and the abrasive particles; and (g)curing the second binder.
 29. A method of preparing a coated abrasivearticle according to claim 28 wherein the first binder is the reactionproduct of the epoxy-containing material and the hydroxyl-terminatedpolyester component.